Currently I find it very hard to evaluate your own personal performance without the use of 3rd party software and deep research into your class performance. I know they do not want to add parsing to the game because they are afraid people will harass others because of their performance.

An easy solution to these problems could be a scoring system to show your overall contribution. Only you can see your score at the end of the dungeon and it would be based off your role. An easy reward would be an exp bonus or tome bonus based off the level of the dungeon and based on the score you get. This would encourage people to play to the best of their abilities and help people who may not be performing well see what areas they need to work on. Harassment would not be an issue because you cant see your "grade" or "score" till after the dungeon is over. Since every role is based off your own personal performance there is no reason to get upset at another player as they will not influence your grade.

The emphasis of a system like this would be personal improvement and rewarding players for playing their best. How you use the system is completely up to you. If you don't care then you can generally ignore it at the end. As with every other system in the game the players that put in more effort will be rewarded. Possible areas to judge each role on could be:

Tank
-Damage per Second (not expected to be as much as dps role)
-Damage Mitigated
-Avoidable Damage Taken

DPS
-Damage per Second
-Avoidable Damage Taken

Healer
-Damage Healed/Shielded
-Damage per Second (not expected to be as much as dps role)
-Avoidable Damage Taken